Wanting a red lens for night work, I realized I had to be resourceful because the light I wanted to fit it to was of an odd size. Red lenses aren't made for all sizes, besides..I like being inventive.
It dawned on me that somebody must make the color of plastic bottle which would make good lens material to suit my needs. Next trip to Walmart, lifting and looking through the unfilled necks of bottles ..to be sure the liquid contained didn't supply ALL the color.
I found the bottle below, and since I used Marvel mystery oil anyway, I bought it. It is a 16 oz bottle, so the contents fit nicely in a 20 Coke bottle, properly labeled with duct tape. Cut it cleaned half with Goo-gone, the other half with fingernail polish remover...made an excellent lens.
In photo below, note that the neck is red, even above the oil level ;
